Synchronization error reduction in common public radio interface (CPRI) passive optical networks (PONs)

Abstract

A first apparatus comprises: a processor configured to generate a first synchronization message; a transmitter coupled to the processor and configured to transmit the first synchronization message to a second apparatus at a first wavelength; and a receiver coupled to the processor and configured to receive a second synchronization message from the second apparatus at a second wavelength and in response to the first synchronization message, the first wavelength and the second wavelength are based on a reduction of a latency difference between the second synchronization message and the first synchronization message, and the processor is further configured to calculate a TO between the first apparatus and the second apparatus based on the reduction.

What is claimed is: 
     
       1. A first apparatus comprising:
 a processor configured to generate a first synchronization message; 
 a transmitter coupled to the processor and configured to transmit the first synchronization message to a second apparatus at a first wavelength; and 
 a receiver coupled to the processor and configured to receive a second synchronization message from the second apparatus at a second wavelength and in response to the first synchronization message, 
 the first wavelength and the second wavelength are based on a reduction of a latency difference between the second synchronization message and the first synchronization message, and 
 the processor is further configured to calculate a timing offset (TO) between the first apparatus and the second apparatus based on the reduction. 
 
     
     
       2. The first apparatus of  claim 1 , wherein the transmitter is further configured to further transmit the first synchronization message through a fiber, and wherein the receiver is further configured to further receive the second synchronization message through the fiber. 
     
     
       3. The first apparatus of  claim 2 , wherein the first wavelength and the second wavelength are approximately symmetric about a zero-dispersion wavelength of the fiber. 
     
     
       4. The first apparatus of  claim 3 , wherein the first wavelength is about 1,357±2 nanometers (nm) and the second wavelength is about 1,270±10 nm, wherein the first wavelength is about 1,331±10 nm and the second wavelength is about 1,291±10 nm, or wherein the first wavelength is about 1,309.14±2 nm and the second wavelength is about 1,295.56±2 nm. 
     
     
       5. The first apparatus of  claim 3 , wherein the first wavelength and the second wavelength are in a same wavelength band, and wherein the wavelength band is centered around the zero-dispersion wavelength. 
     
     
       6. The first apparatus of  claim 1 , wherein the first apparatus is an optical line terminal (OLT) or a baseband unit (BBU), and wherein the second apparatus is an optical network unit (ONU) or a remote radio unit (RRU). 
     
     
       7. The first apparatus of  claim 1 , wherein the first wavelength and the second wavelength are further based on a minimization of the latency difference, and wherein the processor is further configured to further calculate the TO based on the minimization. 
     
     
       8. A method comprising:
 generating a first synchronization message; 
 transmitting the first synchronization message at a first wavelength; 
 receiving a second synchronization message at a second wavelength and in response to the first synchronization message, the first wavelength and the second wavelength are based on a reduction of a latency difference between the second synchronization message and the first synchronization message; and 
 calculating a timing offset (TO) based on the reduction. 
 
     
     
       9. The method of  claim 8 , further comprising:
 further transmitting the first synchronization message through a fiber; and 
 receiving the second synchronization message through the fiber. 
 
     
     
       10. The method of  claim 9 , wherein the first wavelength and the second wavelength are approximately symmetric about a zero-dispersion wavelength of the fiber. 
     
     
       11. The method of  claim 10 , wherein the first wavelength is about 1,357±2 nanometers (nm) and the second wavelength is about 1,270±10 nm, wherein the first wavelength is about 1,331±10 nm and the second wavelength is about 1,291±10 nm, or wherein the first wavelength is about 1,309.14±2 nm and the second wavelength is about 1,295.56±2 nm. 
     
     
       12. The method of  claim 10 , wherein the first wavelength and the second wavelength are in a same wavelength band, and wherein the wavelength band is centered around the zero-dispersion wavelength. 
     
     
       13. The method of  claim 8 , wherein an optical line terminal (OLT) or a baseband unit (BBU) performs the method. 
     
     
       14. The method of  claim 13 , further comprising:
 further transmitting the first synchronization message to an optical network unit (ONU) or a remote radio unit (RRU); and 
 further receiving the second synchronization message from the ONU or the RRU. 
 
     
     
       15. The method of  claim 8 , wherein the first wavelength and the second wavelength are further based on a minimization of the latency difference, and wherein the method further comprises further calculating the TO based on the minimization. 
     
     
       16. A method comprising:
 selecting an upstream wavelength and a downstream wavelength in order to reduce a latency difference between an upstream time delay and a downstream time delay, the upstream time delay is associated with transmission from a first apparatus to a second apparatus, and the downstream time delay is associated with transmission from the second apparatus to the first apparatus; 
 assigning the upstream wavelength to the first apparatus; and 
 assigning the downstream wavelength to the second apparatus. 
 
     
     
       17. The method of  claim 16 , further comprising further selecting the upstream wavelength and the downstream wavelength based on a distance between the first apparatus and the second apparatus. 
     
     
       18. The method of  claim 17 , further comprising further selecting the upstream wavelength and the downstream wavelength based on a zero-dispersion slope. 
     
     
       19. The method of  claim 18 , further comprising further selecting the upstream wavelength and the downstream wavelength based on a zero-dispersion wavelength of a fiber connecting the first apparatus and the second apparatus. 
     
     
       20. The method of  claim 19 , further comprising further selecting the upstream wavelength and the downstream wavelength to be approximately symmetrical about the zero-dispersion wavelength.